Which DACs are known to be sweet/rich/relaxed?

I use REW to measure the room myself.

Why not use it to EQ the offending frequencies? You could use room treatments but in this case I suspect it needs some attenuation at certain frequencies. Much easier to do.  

@robert1976 That recording (and most all of them) of Red Hot Chilly Peppers sounds compressed. It’s the stuff you listen to in the car, in the gym with headphones or as background music at home. Unless I’m missing something myself I never heard the RHCPs sound good on any version of the system I had over the years. That’s just not a good benchmark and your system is basically telling you that. 
Just my $0.02

Hello OP,

I have Nucleus+ > Tambaqui > Audionet PreG2 > Audionet Max amps >  YG Hailey 2.2s.

Changing my cables from (first cheap cables with silver) to Audience AU 24 SX was a big improvement in fullness and warmth. 

Then changing to Kubala Sosna Elation was a huge improvement (full loom).

I thought I was finished.  But I decided to try an Auralic Aries G2.1 as streamer, between my Nucleus + (on network) and now usb to Tambaqui.  this added better imaging, warmth, and seems more lifelike.  Very easy to install and set up, and also easy to compare.  Yes I used all K-S cables on the new streamer (power and usb).

Are you near Maryland?  Ken

Me posting here and asking for feedback is *exactly* that: delving into the source of my problems. I’m open-minded and not fixated on one particular solution or the other. Yes, my budget is substantial, but that does not mean I want to throw mud against the wall and see what sticks. I started this topic to learn.

I use REW to measure the room myself.

I did not mean you, I mean all the effectively "random" suggestions that amount to throwing money at the problem but fortunately sprinkled in, a few suggestions to attempt to get to the heart of the problem.

You already have (assuming working properly) about as perfect a DAC as possible. Anything else will add distortion, frequency response issues, etc. Looking at the ASR test, about the only issue is the slow filter.  If I understand things right, that is only an issue with a flawed recording. Others can probably pipe in better on that. Cymbals have lot of power at high frequency.

How does your REW plot look?  Are there any obvious peaks in the mid-range or high frequencies?

Here is an interesting page with cymbals and a discussion of frequencies with samples. It may be good for trying to isolate the issue.

https://www.musical-u.com/learn/percussion-frequencies-part-2-cymbals/

I listened again to Californication (from that album). The whole track has an edgy sound. I can't say any worse loud or quieter though. It does not sound like the best recording.

Also to consider is if perhaps there is something wrong with your amp or speakers that is highlighted with this music at high volumes. I have had issues in the past that only came out at high volumes (mid-range was failing).

Hmmmm,

I don't know anything about streaming.

Do you have the same source in LP, CD, HiRez Stream?

Is the LP more involving than the CD?

IOW, can you isolate the Streamer from the System Sound?

Have you considered a Tube Preamp?